Simple ebike 'fuel gauge'

[otas]

Cheap and small 5v power supplies : A friend has just loaned me a controller with a cycle analyst plug built in (6 pin connector) which has made me rethink my power options.

For PIC and little associated logic circuit supply I use a drop resistor, zener BZX-C5V1 and ceramic 100nF 50V cap. as a filter. This gives me 5.1V and does not have to be too precise. For 12V I use 2k2 resistor. The PIC is quite happy, and I drive 741 and gate of a MOSFET switch with it.
Cheap and cheerfull, tried and tested on 10-16V.

otto

[otas]

Exactly, but I wanted to KISS - keep it simple s... LED's will start dropping off after approx 70% remaining power, which I think is acceptable. For me at least...

I'm not sure that this will really be the case. I did something similar to lower the trigger voltage of the LEDs on my throttle (I just used a series resistor, as it turns out that the current variation as the LEDs turns on isn't that great) but found that the indication wasn't that reliable. I was running on a pack of Headway LiFePO4 cells at the time, that tended to sag a bit more then LiPo under load, but one thing I noticed was that the LEDs tended to drop as the power came on then recover back at lower power settings. Leaving the bike off for a few minutes would restore the "full power" indication as the cell terminal voltage recovered, even when I knew that the battery pack had to be close to being fully discharged. Trying to interpret the voltage drop under load with the battery charge state was difficult, which is why I opted to build this meter instead.

Jeremy

Jeremy, I agree, this is far from your elegant and precise power meter, I have tried the same, first the drop resistor, which I found not very good, than voltage divider, which had to have relatively small resistances to have the output suitable for 5k ohm "LED voltmeter/indicator". I did not want to waste precious energy on the voltmeter. Therefore my low impedance emitter output with voltage divider in the base. I have just rode the bike and my Zippy's do recover very slightly after a load, but as an indicator of battery voltage it works fine. It shows pretty well the near full, middle and near end of the charge.

otto

[gwhy!]

Exactly, but I wanted to KISS - keep it simple s... LED's will start dropping off after approx 70% remaining power, which I think is acceptable. For me at least...

I'm not sure that this will really be the case. I did something similar to lower the trigger voltage of the LEDs on my throttle (I just used a series resistor, as it turns out that the current variation as the LEDs turns on isn't that great) but found that the indication wasn't that reliable. I was running on a pack of Headway LiFePO4 cells at the time, that tended to sag a bit more then LiPo under load, but one thing I noticed was that the LEDs tended to drop as the power came on then recover back at lower power settings. Leaving the bike off for a few minutes would restore the "full power" indication as the cell terminal voltage recovered, even when I knew that the battery pack had to be close to being fully discharged. Trying to interpret the voltage drop under load with the battery charge state was difficult, which is why I opted to build this meter instead.

Jeremy

Jeremy, I agree, this is far from your elegant and precise power meter, I have tried the same, first the drop resistor, which I found not very good, than voltage divider, which had to have relatively small resistances to have the output suitable for 5k ohm "LED voltmeter/indicator". I did not want to waste precious energy on the voltmeter. Therefore my low impedance emitter output with voltage divider in the base. I have just rode the bike and my Zippy's do recover very slightly after a load, but as an indicator of battery voltage it works fine. It shows pretty well the near full, middle and near end of the charge.

otto

What about using a little picaxe to drive the leds on the throttle ?. That way it could be made precise to drive all 3 (?) leds.

[otas]

What about using a little picaxe to drive the leds on the throttle ?. That way it could be made precise to drive all 3 (?) leds.

Gwhy, there is perhaps a little misunderstanding. The modified throttle indicator works fine with all 4 LEDs working as they should in the max-min-empty display. It has got the usual limitation of estimating the power left by measuring voltage across cells as any voltmeter would have. Slight drawback is, that it still shows HI - as in 100%, when the voltage difference between 4.2V and 3.2V is down to 80%. The middle, low and empty at 32V for 10S 40V pack is shown correctly from this point on.
otto

[gwhy!]

What about using a little picaxe to drive the leds on the throttle ?. That way it could be made precise to drive all 3 (?) leds.

Gwhy, there is perhaps a little misunderstanding. The modified throttle indicator works fine with all 4 LEDs working as they should in the max-min-empty display. It has got the usual limitation of estimating the power left by measuring voltage across cells as any voltmeter would have. Slight drawback is, that it still shows HI - as in 100%, when the voltage difference between 4.2V and 3.2V is down to 80%. The middle, low and empty at 32V for 10S 40V pack is shown correctly from this point on.
otto

Yes ok I see what you mean now. I am not driving the led battery gauge on the throttle myself, but drive 2 leds ( 4 levels )from the picaxe to indicate the drop between 4.2 and 3.2 but now rethinking about using the throttle leds my not be possible because how they are configured.

[yopappamon]

What, no pics of the sacrificial victims, showing their cratered epoxy housings?

There was no excitement, no magic smoke, just wouldn't download once I got it on the right voltage.

I got no change in the fuel level and no current reading on my first ride. I'll switch the shunt leads and see if that's the problem.

[magudaman]

Well I got my software all figured out and the board into a box. My setup is self contained from the controller and would be mounted on the handle bars and just tied to battery voltage and my current hall sensor. The final specs around 30 - 110v, 200a, with a 30ah maximum. Here are a couple photos of the almost finished case, I really wish I would have waited to just make the slot on the mill but I wanted it working NOW

Ps that is a watts up with my current sensor on the line for testing.

[otas]

Hi Magudaman, nice job, shame about the slot. What about drilling individual holes, if no mill is at hand?

otto

[Jeremy Harris]

A technique I've used to make waterproof "windows" for displays, and cover up mishapen cut outs, is to draw a front panel in black with a drawing or CAD programme, leave a white bloc the exact shape you want for a display window, then print it on to a bit of ordinary paper. Next, trim the paper to size and cut out the white block with a very sharp craft knife. Finally, laminate the cut out bit of paper usign a cheap plastic film laminator. This gives you a front panel with a clear window in it that you can just glue on to the box.

Jeremy

[yopappamon]

I swapped the shunt wires and I see the meter move. Yay! I just finished mounting my new MAC hub. Looked over and saw my rim liners setting there. Oops, crap. Oh, well. Too late now. Hope the rhyno rim is smooth enough to not matter.

Off for a test ride.

Thanks for the design, Jeremy!

[spinningmagnets]

Just saw one of these at the LBS. I think it was $6, aluminum, intended to mount a standard drink "bottle cage" onto the handlebars. One thing I like about it, is that it can be attached without removing the grips or any other thing from the handlebars. If its too tall, you can easily cut off one of its ears (I dub thee, the "Van Gogh" mount), $4 plus tax & shipping:

http://yhst-84224226242177.stores.yahoo.net/vohatowaboca.html

[kfong]

All this crappy weather lately has brought me indoors as well as the need to finish 2 scooters I had promised my nieces. I really like the simple meter Jeremy had found and decided that was the perfect meter for the razor e300 scooters. I wanted something simple enough for them to follow without numbers. I decided to use pics, since I have a whole development platform for it. I will use a smaller pic for the final layout as well as incorporate a low voltage cutoff circuit.

Currently it’s working fine on my desk, just working out features to add. This meter worked out well for this project.

[dhabicht1]

Jeremy,

I love your "fuel gauge" it is exactly what I was looking for. Do you sell these at all? I have tried to search online in the forums but have not been able to find one. Please let me know what the cost is and I could send you payment via PayPal.

Thanks,

Doug

[marty]

Doug,
Jeremy took some time off from bicycle stuff so he could have move time to build a new house for him self. His last post was Sun Dec 25, 2011

Why don't you build a Simple ebike 'fuel gauge' ? and I will buy one from you.

[dhabicht1]

Thanks for the info Marty, where are you from in Buffalo? I live in FL now but grew up In Alden